1. Field of the Invention
The present invention relates to a color purity and convergence magnet for adjusting the static characteristics of the color purity and convergence of a color cathode ray tube and, more particularly to a color purity and convergence magnet capable of fine-adjusting the running paths of the electron beams irrespective of the position of the axial direction of the tube, reducing the influence of its adjusting magnetic field on the electron beams and improving the workability when manufacturing the color cathode ray tube.
2. Description of the Background Art
Generally, in a color cathode ray tube having an electron gun with a structure of in-line arrangement, a color purity and convergence magnet (PCM) is composed of two-pole, four-pole and six-pole magnets. The two-pole magnet adjusts the color purity, the four-pole magnet adjusts the mutual position of two outer electron beams, that is, R/B electron beams, and the six-pole magnet adjusts the mutual position of a central electron beam and two outer electron beams, that is, R/G and B/G electron beams, thereby adjusting the static characteristics of the color purity and convergence of the color cathode ray tube. Each of these magnets is formed in a pair in order to adjust finely the color purity and convergence.
A four-pole magnet widely utilized in the conventional art is illustrated in FIG. 1 and FIGS. 2a through 2b. As illustrated therein, the four-pole magnet consists of a pair of front and rear rings 11 and 12 having a predetermined width. As illustrated in FIG. 1, the front and rear rings 11 and 12 are mounted on the neck portion 1 of the tube in a longitudinal direction of the cathode ray tube. The rear ring 12 is formed to have a magnetic field about 1.1xcx9c1.3 times stronger than that of the front ring 11. The two-pole and six-pole magnets are formed in the same manner. This difference between the magnetic fields formed at the front and rear rings 11 and 12 is obtained by considering components of velocity acquired when electrons are accelerated in the electron gun.
However, such configuration is disadvantageous for the following reasons. Firstly, since a pair of magnets on which a certain magnetic field is formed influence the electron beams differently depending on their position, an optimum adjustment may be made only at a position corresponding to the difference between the magnetic fields formed at the front and rear rings 11 and 12.
Secondly, since a certain magnetic field was already formed in each of the front and rear rings, it influences the electron beams even in the case that adjustment is not required.
In other words, at any random position at which a composite magnetic field in front-rear arrangement is accelerated from the axial direction of the tube to the screen direction, the magnetic field cannot be close to zero and thus this adjustment becomes difficult. Generally, two-pole, four-pole and six-pole magnetic fields or electric fields have a problem of distorting the shape of electron beams. Among them, the four-pole magnetic field is most fatal. Moreover, there is another problem that it is difficult to achieve the fine adjustment required in an ITC process of combining a cathode ray tube and a deflection yoke.
In order to solve the above problems, Japanese patent application laid-open publication No. Sho 51-65830 (Jun. 7, 1976) discloses a magnetic beam adjusting device for use in a cathode ray tube that is not arranged forward and backward in a longitudinal direction of the tube, but arranged to overlap in a radial direction as illustrated in FIGS. 3 and 4.
In the conventional beam adjusting device as illustrated in FIGS. 3 and 4, two four-pole ring-shaped magnets 1A and 1B in a pair are formed, for example, by using a binder made of rubber and synthetic resin and injecting powdered magnet material such as barium ferrite into the binder. The pair of magnets have different inner diameters and are combined in a state in which they are double-sided in and out, with one direction at the inner side and the other direction at the outer side, and relative rotation is freely performed. To ensure this combination, a flange 2 is formed at one end of the inner ring-shaped magnet 1A, and the outer ring-shaped magnet 1B is fixedly fitted to a step portion formed along the outer circumferential surface of the flange 2.
This pair of ring-shaped magnets 1A and 1B are mounted on the neck portion of the picture tube, and both magnets 1A and 1B are positioned at the same surface orthogonal to the tube axis. Both ring-shaped magnets 1A and 1B have four magnetic poles arranged at the same interval from each other in a circumferential direction, with alternating polarity. These magnetic fields are installed at the outer surface of the inner ring-shaped magnet 1A and at the inner surface of the outer ring-shaped magnet 1B, so that they are opposed to the surface of contact between the inner and outer ring-shaped magnets 1A and 1B. Herein, the reference numerals 3 and 4 indicate hand levers for rotation control of the ring-shaped magnets 1A and 1B, respectively.
By this construction, the magnetic field in the tube can be remained in a zero state, thereby an accurate adjustment becomes possible, leakage flux minimally influences on the interior of the picture tube, and, further, the length in the axial line direction can be decreased.
In addition, as an example of an another conventional art, Japanese patent application laid-open publication No. Hei 4-181638 (Jun. 29, 1992) discloses a convergence purity correction apparatus as illustrated in FIGS. 5a-5c and FIG. 6.
In FIGS. 5a and 5b, a two-pole magnet 40A and a four-pole magnet 40B are combined on the same surface. For this reason, the axial length for a pair of ring magnets is decreased, and the back space for a deflection yoke can be set as large as the decreased length as compared to the conventional art. Thus, it is possible to sufficiently back the deflection yoke toward the electron gun assembly during color purity adjustment for the cathode ray tube, and it is easy to perform the color purity adjustment.
Also, in a composite ring magnet 40A as illustrated in FIG. 6, a two-pole magnet 40A1 having an inner diameter larger than that of a ring type four-pole magnet 40B having almost the same inner and outer diameters as in the conventional art is co-axially attached to the same surface as the four-pole magnet 40B, with a rotary ring 40D1 intercalated to the outer diameter of the four-pole magnet 40B, and another two-pole magnet 40A2 is co-axially attached to the same surface as the four-pole magnet 40B and the two-pole magnet 40A1, with a rotary ring 40D2 intercalated to the outer diameter of the two-pole magnet 40A1.
In this structure, the rotary rings 40D1 and 40D2 are constructed in such a manner that they can rotate freely, independently and smoothly, being interlocked with an H-type sphere at the inner and outer diameter portions of the rotary rings 40D1 and 40D2 and a protruding portion formed at the inner and outer diameter portions of the four-pole magnet 40B and the two-pole magnets 40A1 and 40A2. In a ring portion at the outer diameter of the two-pole magnets 40A1 and 40A2 and four-pole magnet 40B, respective hand levers are constructed such that they are formed as a single body to thereby perform rotation adjustment conveniently.
By the construction as above described in which the two-pole magnets and the four-pole magnet are combined and the two-pole magnets are arranged at the outer sides of the four-pole magnet, a back space for the deflection yoke can be obtained, and the axial length of the magnetic correcting device can be reduced. Moreover, by enlarging the inner diameter of the two-pole magnet, a parallel uniform magnetic field can be obtained in a region where electron beams exist, thereby eliminating the deformation of a section of an electron beam spot and preventing degradation in focus characteristics.
In addition, the construction of a magnetic correction device for use in a cathode ray tube as disclosed in Japanese patent application laid-open publication Nos. Sho 50-12964 (Feb. 10, 1975) and Sho 50-57725 (May 20, 1975) is illustrated in FIGS. 7a through 7b. 
In FIGS. 7a and 7b, the magnetic correction device for use in a cathode ray tube is characterized in that, in a magnetic correction apparatus provided with: at least one support member 47 made of nonmagnetic material; a fixing member for fixing the support member to the neck portion of the cathode ray tube; and at least one pair of coaxial rings with magnetic poles distributed and arranged adjacent their borders for thereby mounting the coaxial rings on the electric support member and at the same time controlling the passage of electron beams generated from the cathode ray tube wherein rotation is freely performed in the opposite direction while centering around the axis of the rings, the inner diameter of a ring 43 at one side of a pair of coaxial rings is set larger than the outer diameter of a ring 45 at the other side, the small-diameter ring 45 is mounted on the large-diameter ring 43, a saw tooth 49 is installed at the inner circumferential surface of the outer-diameter ring 43, a saw tooth 51 is installed at the outer diameter of the inner-outer ring 45, and at least one pinion 53 capable of rotating around a spindle 55 fixed to the electric support member 47 and at the same time corresponding to the saw teeth 49 and 51 is arranged in a space portion between both rings 43 and 45.
By this construction, the axial dimension of the correction apparatus can be reduced, and the strength of a magnetic field is easily adjustable by automatically rotating the inner ring in the reverse direction by rotation of the outer ring.
In the above-described constructions in the conventional art, the workability for manufacturing the color cathode ray tube can be increased because the elements are arranged to overlap with each other in the radial direction of the cathode ray tube. However, there arises problem that it is not easy to form a magnetic pole on the outer surface compared to the inner surface, it is impossible to perform fine adjustment according to the difference between the amounts of magnetization toward the inner surface and outer surface because it is difficult to control each of the amounts of magnetization, and the influence of a magnetic field on electron beams cannot be reduced.
Accordingly, in order to overcome the above-described problems, it is an object of the present invention to provide a color purity and convergence magnet for a color cathode ray tube that can form a zero composite magnetic field capable of satisfying the minimum amount of beam movement and finely adjust the speed and distortion degree of beams on any position on the tube axis by minimizing the magnet""s influence on the beams, when the magnet is mounted on a certain position at the neck portion. Also, the object of the present invention is to provide a color purity and convergence magnet for a color cathode ray tube that can shorten the neck portion even in a large-sized cathode ray tube and largely improve the workability in neck portion during a fabrication process of the cathode ray tube.
In order to achieve the above object, in accordance with the present invention, A color purity and convergence magnet for a color cathode ray tube comprising an inner ring magnet and an outer ring magnet being mounted at the outer circumference of a neck portion in the tube and arranged externally and internally in a radial direction on the same surface orthogonal to the tube axis so as to adjust the static characteristics of the color purity and convergence, wherein a magnetic force of the same number of poles such as two-pole, four-pole and six-pole is formed at the same angle of the circumference is characterized in that the inner surface of the inner ring magnet is magnetized, and the magnetizing force of the inner ring magnet is smaller than that of the outer ring magnet in a strength.
It is preferable that the outer ring magnet is magnetized to its inner surface, and the magnetization intensity of the outer ring magnet is M0=(xcex12/xcex2)MI with respect to the magnetization intensity of the inner ring magnet (herein, xcex1 is R0/RI, xcex2 is V0/VI, RI is the internal radius of the inner ring magnet, R0 is the internal radius of the outer ring magnet 22, VI is the magnetic volume of the inner ring magnet, and V0 is the magnetic volume of the outer ring magnet). The adjusting hand lever of the inner ring magnet can be formed to protrude outwardly in a radial direction, being protruded in the axial direction of the tube from one surface vertical to a tube axis of the inner ring magnet, and the adjusting hand lever of the outer ring magnet can be formed to protrude from the outer circumferential surface of the outer ring magnet so that it is close to the adjusting hand lever of the inner ring magnet, when combined with the inner ring magnet.
In addition, it is configurable that the amount of electron beams movement is less than 0.5 mm, when the outer ring magnet and inner ring magnet are arranged so that magnetizing force of the opposite polarity corresponds towards the radial direction.